The several experiments in this project relate to the common theme of discovery and delineation of the factors that determine and modify susceptibility to carcinogenesis. An interdisciplinary approach to analysis of the effect of the common environmental carcinogen N-nitrosodimethylamine (NDMA) has been fruitful. Striking effects of ethanol, which is being increasingly implicated in the etiology of human cancers, has been demonstrated. Co- administration of ethanol in the drinking water with NDMA has been found to cause a consistent and significant increase in numbers of lung tumors and in promutagenic DNA adducts in the lung. Tumor promotion by ethanol was ruled out as a contributing factor. Competitive inhibition of the liver enzyme acting on NOMA, a demethylase (cytochrome P-450j) is the postulated mechanism. This enzyme has been studied biochemically and pharmacokinetically in mouse, monkey, and several other species, with inhibition by a specific monoclonal antibody to confirm the nature of the P-450. The activity appears to be highly conserved across species, so that results from the mouse have particular relevance to the human. Utilization of this system is ongoing. Interesting results have also been obtained with N-nitrosocimetidine (NCM), derivative of a commonly-used pharmaceutical. Though not a complete carcinogen, this alkylating agent both enhanced progression of preformed skin papillomas to malignancy and initiated cells which could be caused to develop by subsequent application of a tumor promoter. These NCM-initiated tumors were all found to contain DNA that transformed 3T3 cells and were mutated in the second position of codon 61 of the H-ras oncogene. Other experiments that are ongoing in this project include immunohistochemical studies of localization of cytochromes P-450 and of DNA adducts using monoclonal antibody reagents, and investigation of the protective effect in vivo of pretreatment of mice with inducers of enzymes metabolizing carcinogens.